Unplanned Extubations in Pediatric Critical Care: A Case–Control Study

The aim of this study was to quantify associations between the risk of unplanned extubation and patient-, environment-, and care-related factors in pediatric critical care and to compare outcomes between children who did and did not experience an unplanned extubation. This is a retrospective case–control analysis including patients <18 years who experienced an unplanned extubation during intensive care unit (ICU) admission (2004–2014). Cases were matched by age, duration of mechanical ventilation, and date to control patients (4:1) who were intubated but did not experience an unplanned extubation. Conditional logistic regression was used to evaluate associations between unplanned extubations and the abstracted characteristics. We identified 1,601 eligible controls matched to 458 case patients. When adjusted for confounders, eight variables were associated with unplanned extubation: three patient-related factors (previous ICU admission, previous intubation, and the volume of secretions); one environment-related factor (patient room setup); and four care-related factors (intubation route, and the use of sedation, muscle relaxation, and restraints). Patients who had an unplanned extubation had longer length of stay, but lower rate of mortality. This is the largest case–control study identifying variables associated with unplanned extubation in pediatric critical care. Several are potentially modifiable and may provide opportunities to improve quality of care in controlled ICU environments.

Risk factors for unplanned paediatric intensive care unit admission after anaesthesia—an international multicentre study

Objectives

Unplanned intensive care unit (ICU) admissions are associated with near-miss events, morbidity, and mortality. We describe the rate, resource utilization, and outcomes of paediatric patients urgently admitted directly to ICU post-anaesthesia compared to other sources of unplanned ICU admissions.

Methods

We performed a secondary analysis of data from specialist paediatric hospitals in 7 countries. Patients urgently admitted to the ICU post-anaesthesia were combined and matched with 1 to 3 unique controls from unplanned ICU admissions from other locations by age and hospital. Demographic, clinical, and outcome variables were compared using the Wilcoxon rank-sum test for continuous variables and chi-square or Fisher’s exact test for categorical variables. The effect of admission sources on binary outcomes was estimated using univariable conditional logistic regression models with stratification by matched set of anaesthesia and non-anaesthesia admission sources.

Results

Most admissions were &lt;1 year of age and for respiratory reasons. Admissions post-anaesthesia were shorter, occurred later in the day, and were more likely to be mechanically ventilated. Admissions post-anaesthesia were less likely to have had a previous ICU admission (4.8% compared to 11%, P=0.032) or PIM ‘high-risk diagnosis’ (9.5% versus 17.2%, P=0.035) but there was no difference in the number of subsequent ICU admissions. There was no difference in the PIM severity of illness score and no mortality difference between the groups.

Conclusions

Young children and respiratory indications dominated unplanned ICU admissions post-anaesthesia, which was more likely later in the day and with mechanical ventilation.

Dosing of enteral acetaminophen in critically ill children: a cohort study

OBJECTIVE

Acetaminophen is the most common medication prescribed in children's hospitals. The aim of the study was to estimate the frequency and risk factors for acetaminophen underdosing and overdosing in the paediatric intensive care unit (PICU).

DESIGN

Retrospective cohort of drug administrations in a large tertiary care PICU.

PATIENTS

All PICU admissions, less than 18 years of age, admitted between 1 January 2008 and 1 January 2018, having received at least one dose of enteral acetaminophen.

METHODS

The primary outcome was acetaminophen underdosing and overdosing, defined as doses exceeding the 10% upper and lower limits of the standard reference range (10-15 mg/kg) and 10% above daily maximum dose (75 mg/kg). A generalised estimating equation regression assessed patient risk factors for single underdosing, single overdosing and cumulative daily overdosing of acetaminophen.

RESULTS

Of the 147 485 doses of enteral acetaminophen administered, 7814 (5.3%) were single underdoses (1 in every 19 doses) and 4640 (3.1%) were single overdoses (1 in every 32 doses). There were 6813 cumulative overdose days (1 in every 9 patient-days). Risk factors for both underdosing and overdosing included older age and cardiac admission, whereas risk factors for cumulative overdosing were young age and cardiac admission. Electronic prescribing increased the risk of underdosing and overdosing, but decreased cumulative acetaminophen overdosing (relative risk 0.51, p=0.001).

CONCLUSION

Acetaminophen underdosing and overdosing are common in the PICU and can be detected with pharmacoepidemiology. Electronic prescribing increased the risk of single underdosing and overdosing, although it reduced the risk of cumulative overdosing.

Death and Dying in Hospitalized Pediatric Patients: A Prospective Multicenter, Multinational Study

Background: For hospitalized children admitted outside of a critical care unit, the location, mode of death, "do-not-resuscitate" order (DNR) use, and involvement of palliative care teams have not been described across high-income countries. Objective: To describe location of death, patient and terminal care plan characteristics of pediatric inpatient deaths inside and outside the pediatric intensive care unit (PICU). Design: Secondary analysis of inpatient deaths in the Evaluating Processes of Care and Outcomes of Children in Hospital (EPOCH) randomized controlled trial. Setting/Subjects: Twenty-one centers from Canada, Belgium, the United Kingdom, Ireland, Italy, the Netherlands, and New Zealand. Measurement: Descriptive statistics were used to compare patient and terminal care plan characteristics. A multivariable generalized estimating equation examined if palliative care consult during hospital admission was associated with location of death. Results: A total of 365 of 144,539 patients enrolled in EPOCH died; 219 (60%) died in PICU and 143 (40%) died on another inpatient unit. Compared with other inpatient wards, patients who died in PICU were less likely to be expected to die, have a DNR or palliative care consult. Hospital palliative care consultation was more common in older children and independently associated with a lower adjusted odds (95% confidence interval) of dying in PICU [0.59 (0.52-0.68)]. Conclusion: Most pediatric inpatient deaths occur in PICU where patients were less likely to have a DNR or palliative care consult. Palliative care consultation could be better integrated into end-of-life care for younger children and those dying in PICU.

Magnetic Resonance Imaging Findings Are Associated with Long-Term Global Neurological Function or Death after Traumatic Brain Injury in Critically Ill Children

The identification of children with traumatic brain injury (TBI) who are at risk of death or poor global neurological functional outcome remains a challenge. Magnetic resonance imaging (MRI) can detect several brain pathologies that are a result of TBI; however, the types and locations of pathology that are the most predictive remain to be determined. Forty-two critically ill children with TBI were recruited prospectively from pediatric intensive care units at five Canadian children's hospitals. Pathologies detected on subacute phase MRIs included cerebral hematoma, herniation, cerebral laceration, cerebral edema, midline shift, and the presence and location of cerebral contusion or diffuse axonal injury (DAI) in 28 regions of interest were assessed. Global functional outcome or death more than 12 months post-injury was assessed using the Pediatric Cerebral Performance Category score. Linear modeling was employed to evaluate the utility of an MRI composite score for predicting long-term global neurological function or death after injury, and nonlinear Random Forest modeling was used to identify which MRI features have the most predictive utility. A linear predictive model of favorable versus unfavorable long-term outcomes was significantly improved when an MRI composite score was added to clinical variables. Nonlinear Random Forest modeling identified five MRI variables as stable predictors of poor outcomes: presence of herniation, DAI in the parietal lobe, DAI in the subcortical white matter, DAI in the posterior corpus callosum, and cerebral contusion in the anterior temporal lobe. Clinical MRI has prognostic value to identify children with TBI at risk of long-term unfavorable outcomes.

Describing drug and fluid therapy in the paediatric intensive care unit: A pilot study

PURPOSE

Care in the paediatric intensive care unit (PICU) involves many clinical activities. The objectives of this study were to evaluate the feasibility of a novel observation method, the reliability of data abstraction, and to report the initial findings from application of this approach.

MATERIALS AND METHODS

Bedside activities of patients and clinical staff were recorded by direct observational study using video recording and audio annotation. Data were abstracted into 9 broad clinical activities and 12 specific drug-fluid activities. Enrolment rates, agreement between abstractors, clinical activity durations and interruptions are reported.

RESULTS

We enrolled 42 healthcare professionals, 12 family members of 13 patients, and recorded 12 patients (consent rates of 70%-92%). There were 884 clinical activity episodes. Each hour was comprised of a median (IQR) of 11.9 (4.8-16.5) minutes of drug and fluid related tasks. The 682 drug and fluid related activities were mainly preparation and administration. Interruptions occurred on average 7 times per hour. Data abstraction for 8 h had intra-class correlation co-efficient (95% CI) of 0.91 (079-0.96).

CONCLUSIONS

Real-time recording of clinical tasks in the PICU using a direct observation model combined with video recording is feasible. Preliminary results suggest abundant and diverse activity is routine.

Incidence, outcomes and outcome prediction of unplanned extubation in critically ill children: An 11year experience

PURPOSE

Unplanned extubation represents loss of control in the ICU, is associated with harm and is used as a measure of quality of care. We evaluated the rates and consequences of unplanned extubation.

MATERIALS AND METHODS

Eligible patients were intubated, <18years, and in ICU. Patient, care-related and environmental characteristics were compared in patients who did and did not receive positive pressure ventilation in the 24h after events. Rates are expressed per 100 intubation-days.

RESULTS

The 11,310 eligible patient-admissions identified were intubated for 75,519days; 410 (3.39%) patients had 458 unplanned extubation events (0.61 events/100 intubation-days). Annual rates of unplanned extubation reduced from 0.98 in 2004 to 0.37 in 2014. Consequences occurred in 245 (53.5%) events and included cardiac arrest in 9 (2%), bradycardia 52 (11%), and stridor 63 (14%). Positive pressure was provided after 263 (57%) events, and was independently associated with pre-event sedative and muscle relaxant drugs, non-use of restraints, respiratory reason for intubation and recent care by more nurses.

CONCLUSION

Unplanned extubation was associated with both significant and no morbidity. Modification of factors including more consistent nurse staffing, restraint use, and increased vigilance in patients with previous events may potentially reduce rates and adverse consequences of unplanned extubation.

Brain biomarkers and pre-injury cognition are associated with long-term cognitive outcome in children with traumatic brain injury

Background

Children with traumatic brain injury (TBI) are frequently at risk of long-term impairments of attention and executive functioning but these problems are difficult to predict. Although deficits have been reported to vary with injury severity, age at injury and sex, prognostication of outcome remains imperfect at a patient-specific level. The objective of this proof of principle study was to evaluate a variety of patient variables, along with six brain-specific and inflammatory serum protein biomarkers, as predictors of long-term cognitive outcome following paediatric TBI.

Method

Outcome was assessed in 23 patients via parent-rated questionnaires related to attention deficit hyperactivity disorder (ADHD) and executive functioning, using the Conners 3rd Edition Rating Scales (Conners-3) and Behaviour Rating Inventory of Executive Function (BRIEF) at a mean time since injury of 3.1 years. Partial least squares (PLS) analyses were performed to identify factors measured at the time of injury that were most closely associated with outcome on (1) the Conners-3 and (2) the Behavioural Regulation Index (BRI) and (3) Metacognition Index (MI) of the BRIEF.

Results

Higher levels of neuron specific enolase (NSE) and lower levels of soluble neuron cell adhesion molecule (sNCAM) were associated with higher scores on the inattention, hyperactivity/impulsivity and executive functioning scales of the Conners-3, as well as working memory and initiate scales of the MI from the BRIEF. Higher levels of NSE only were associated with higher scores on the inhibit scale of the BRI.

Conclusions

NSE and sNCAM show promise as reliable, early predictors of long-term attention-related and executive functioning problems following paediatric TBI.

Concurrent intravenous drug administration to critically ill children: Evaluation of frequency and compatibility

PURPOSE

To evaluate the frequency of concurrent drug administration and drug-drug incompatibility of concurrently administered drugs in critically ill children based on available references.

MATERIALS AND METHODS

We retrospectively evaluated concurrent intravenous drug administration in children admitted to a single centre. Eligible patients included those admitted to the critical care unit for at least 6-hours in the ten-year period ending 30 July 2015 and received two or more IV drug administrations. Compatibilities were classified using local reference documents.

RESULTS

The 16,863 eligible patients were admitted to ICU for 2,212,326h and received 3,664,667 concurrent administrations. Concurrent infusions ran for 6,263,600h. There were 2,284,066 (62%) concurrent administrations; 334,144 (9%) were compatible, 293,856 (8%) were incompatible, 293,856 (8%) required pharmacist consultation, and 752,601 (21%) had 'unknown' compatibility. Individual patients received a median (IQR) of 33 (10-132) concurrent administrations, comprised of 7 (1-30) concurrent injections 1 (0-5) concurrent infusions and 13 (0-74) concurrently administered injections and infusions.

CONCLUSIONS

Concurrent IV-drug administration is frequent in critically ill children. Known incompatible concurrent administration occurs, however the compatibilities of many drug-drug pairs were unknown - adding complexity to routine bedside management and identifying information gaps for future research.

Seizure burden is independently associated with short term outcome in critically ill children

Seizures are common among critically ill children, but their relationship to outcome remains unclear. We sought to quantify the relationship between electrographic seizure burden and short-term neurological outcome, while controlling for diagnosis and illness severity. Furthermore, we sought to determine whether there is a seizure burden threshold above which there is an increased probability of neurological decline. We prospectively evaluated all infants and children admitted to our paediatric and cardiac intensive care units who underwent clinically ordered continuous video-electroencephalography monitoring over a 3-year period. Seizure burden was quantified by calculating the maximum percentage of any hour that was occupied by electrographic seizures. Outcome measures included neurological decline, defined as a worsening Paediatric Cerebral Performance Category score between hospital admission and discharge, and in-hospital mortality. Two hundred and fifty-nine subjects were evaluated (51% male) with a median age of 2.2 years (interquartile range: 0.3 days-9.7 years). The median duration of continuous video-electroencephalography monitoring was 37 h (interquartile range: 21-56 h). Seizures occurred in 93 subjects (36%, 95% confidence interval = 30-42%), with 23 (9%, 95% confidence interval = 5-12%) experiencing status epilepticus. Neurological decline was observed in 174 subjects (67%), who had a mean maximum seizure burden of 15.7% per hour, compared to 1.8% per hour for those without neurological decline (P < 0.0001). Above a maximum seizure burden threshold of 20% per hour (12 min), both the probability and magnitude of neurological decline rose sharply (P < 0.0001) across all diagnostic categories. On multivariable analysis adjusting for diagnosis and illness severity, the odds of neurological decline increased by 1.13 (95% confidence interval = 1.05-1.21, P = 0.0016) for every 1% increase in maximum hourly seizure burden. Seizure burden was not associated with mortality (odds ratio: 1.003, 95% confidence interval: 0.99-1.02, P = 0.613). We conclude that in this cohort of critically ill children, increasing seizure burden was independently associated with a greater probability and magnitude of neurological decline. Our observation that a seizure burden of more than 12 min in a given hour was strongly associated with neurological decline suggests that early antiepileptic drug management is warranted in this population, and identifies this seizure burden threshold as a potential therapeutic target. These findings support the hypothesis that electrographic seizures independently contribute to brain injury and worsen outcome. Our results motivate and inform the design of future studies to determine whether more aggressive seizure treatment can improve outcome.

Impact of hypotension and low cerebral perfusion pressure on outcomes in children treated with hypothermia therapy following severe traumatic brain injury: a post hoc analysis of the Hypothermia Pediatric Head Injury Trial

Hypotension and low cerebral perfusion pressure are known to be associated with unfavorable outcome in children and adults with traumatic brain injury. Using the database from a previously published, randomized controlled trial of 24 h of hypothermia therapy in children with severe traumatic brain injury, we compared the number of patients with hypotension or low cerebral perfusion pressure between the hypothermia therapy and normothermia groups. We also determined the association between these physiologic insults and unfavorable outcome using regression analysis. There were more patients with episodes of hypotension or low cerebral perfusion pressure in the hypothermia therapy group than in the normothermia group. These physiologic insults were associated with unfavorable outcome in both intervention groups. Hypotension and low cerebral perfusion pressure should be anticipated and prevented in future trials of hypothermia therapy in patients with traumatic brain injury.

Pharmacotherapy in pediatric critical illness: a prospective observational study

BACKGROUND AND OBJECTIVES

Pharmacotherapy is an under-evaluated element of critical care medicine. In order to better understand pharmacotherapy in pediatric critical illness, we evaluated a cohort of emergency admissions to a university-affiliated pediatric intensive care unit (PICU).

METHODS

A prospective, observational study was performed. Eligible patients were admitted to this medical-surgical ICU for at least 24 hours. The primary outcomes were the number of drug orders written, the number of different medications ordered, and the number of drug administrations. Multiple regression analyses were used to identify factors independently associated with each primary outcome.

RESULTS

We studied 100 patients with a median age of 40 months (interquartile range [IQR] 9-82), who were admitted for a total of 851 ICU days. These patients received 4419 drug orders and 11 911 intermittent dose-administrations of 241 different medications. Each patient received a median of 29.5 (IQR 16.5-48.5) drug orders, 14 (IQR 9-18.5) different medications, and 58 (IQR 28-129) drug administrations while in the ICU. The most frequent orders were for morphine 457 (10.6%), furosemide (frusemide) 337 (7.8%), potassium 237 (5.5%), lorazepam 226 (5.2%), and albuterol (salbutamol) 158 (3.7%). The duration of PICU stay and severity of illness were independently associated with all primary outcomes.

CONCLUSIONS

Pharmacotherapy is an active component in the practice of pediatric critical care medicine. We demonstrated that increasing numbers of ordered medications, drug orders, and drug administrations were associated with increasing duration of ICU therapies and the length of ICU stay. These data underscore the potential importance of improved safety and efficacy of medicines used to treat critically ill children.

Safety and efficacy of ketorolac in children after cardiac surgery

OBJECTIVE

To evaluate the nephrotoxic and opioid-sparing effects of ketorolac in children after cardiac surgery.

DESIGN

A retrospective cohort study.

SETTING

A Cardiac Critical Care Unit in a university-affiliated children's hospital.

SUBJECTS

Children less than 18 years of age who underwent low-risk cardiac surgery from July 2002 to December 2005.

RESULTS

Among 248 children studied, 108 received ketorolac and 140 did not. The ketorolac group was older, included a larger proportion of atrial septum defect repairs and a smaller proportion of ventricular septum defect repairs compared to the control group. The median change in serum creatinine did not differ between the ketorolac group and the control group (% change [IQR]); 12% [1-25] increase versus 12% [-3 to 31] increase, P = 0.86. On postoperative day 0 or 1, the ketorolac group received less opioids than control group. There was no difference in duration of mechanical ventilation or in length of stay between groups.

CONCLUSION

Ketorolac started in the first 12 h after a low-risk cardiac surgery in children is not associated with a measurable difference in renal function. The data suggest that ketorolac may be effective in reducing the exposure to opioids. Further studies are required to define subsets of children after cardiac surgery who could safely benefit from ketorolac therapy to reduce pain.

Effect of a sustained inflation on regional distribution of gas and perfluorocarbon during partial liquid ventilation

OBJECTIVE

To study the effect of a sustained inflation (SI) maneuver on the regional distribution of gas and perfluorocarbon (PFC) during partial liquid ventilation (PLV) in normal pigs using computerized densitometry.

STUDY DESIGN

Observational study.

SETTING

Animal research laboratory.

PARTICIPANTS

Three healthy anaesthetized pigs.

INTERVENTIONS

Partial liquid ventilation, lung recruitment, CT densitometry.

METHODOLOGY

Lungs were filled with PFC to "liquid functional residual capacity (FRC)" (35-41 ml/kg) and CT images were recorded at a series of predetermined airway pressure levels (0, 20, 30, 40 cm H2O) both before and after SI to an airway pressure of 40 cm H2O for 30 sec. Anterior, middle, and posterior regions from upper (apical lung) to lower (basal lung) CT slices were analyzed at each pressure level for Hounsfield units to describe the relative distribution of gas and PFC before and after SI. Using an occlusion technique true gas volume above FRC was determined at each pressure level, before and after SI, and a pressure-volume (gas) envelope determined for each animal.

RESULTS

At low airway pressures (<20 cm H2O) gas was distributed predominantly to the anterior (non-dependent) part of the lung and PFC predominantly to the posterior (dependent) lung. Gas and liquid were more uniformly distributed throughout the lung at airway pressures >20 cm H2O. Generation of a pressure-volume (gas) envelope for each animal demonstrated an increase in total gas volume above FRC at each pressure level following recruitment of the lung with SI. However, marked regional differences were evident with the greatest effects of SI seen at higher airway pressures in posterior and basal regions.

CONCLUSION

The healthy PFC filled lung demonstrates an increase in total gas volume following SI. CT densitometry suggests marked heterogeneity of gas/PFC distribution between different regions of lung and heterogeneity of response to SI.

Atelectasis Causes Alveolar Injury in Nonatelectatic Lung Regions

RATIONALE

Many authors have suggested that the mechanism by which atelectasis contributes to injury is through the repetitive opening and closing of distal airways in lung regions that are atelectatic. However, neither the topographic nor mechanistic relationships between atelectasis and distribution of lung injury are known.

OBJECTIVES

To investigate how atelectasis contributes to ventilator-induced lung injury.

METHODS

Surfactant depletion was performed in anesthetized rats that were then allocated to noninjurious or injurious ventilation for 90 min.

MEASUREMENTS

Lung injury was quantified by gas exchange, compliance, histology, wet-to-dry weight, and cytokine expression, and its distribution by histology, stereology, cytokine mRNA expression, in situ hybridization, and immunohistochemistry. Functional residual capacity, percent atelectasis, and injury-induced lung water accumulation were measured using gravimetric and volumetric techniques.

MAIN RESULTS

Atelectasis occurred in the dependent lung regions. Injurious ventilation was associated with alveolar and distal airway injury, while noninjurious ventilation was not. With injurious ventilation, alveolar injury (i.e., histology, myeloperoxidase protein expression, quantification, and localization of cytokine mRNA expression) was maximal in nondependent regions, whereas distal airway injury was equivalent in atelectatic and nonatelectatic regions.

CONCLUSIONS

These data support the notion that lung injury associated with atelectasis involves trauma to the distal airways. We provide topographic and biochemical evidence that such distal airway injury is not localized solely to atelectatic areas, but is instead generalized in both atelectatic and nonatelectatic lung regions. In contrast, alveolar injury associated with atelectasis does not occur in those areas that are atelectatic but occurs instead in remote nonatelectatic alveoli.

Remote ischaemic preconditioning protects against cardiopulmonary bypass-induced tissue injury: a preclinical study

OBJECTIVES

To test the hypothesis that remote ischaemic preconditioning (rIPC) reduces injury after cardiopulmonary bypass (CPB).

DESIGN

Randomised study with an experimental model of CPB (3 h CPB with 2 h of cardioplegic arrest). Twelve 15 kg pigs were randomly assigned to control or rIPC before CPB and followed up for 6 h.

INTERVENTION

rIPC was induced by four 5 min cycles of lower limb ischaemia before CPB.

MAIN OUTCOME MEASURES

Troponin I, glial protein S-100B, lactate concentrations, load-independent indices (conductance catheter) of systolic and diastolic function, and pulmonary resistance and compliance were measured before and for 6 h after CPB.

RESULTS

Troponin I increased after CPB in both groups but during reperfusion the rIPC group had lower concentrations than controls (mean area under the curve -57.3 (SEM 7.3) v 89.0 (11.6) ng.h/ml, p = 0.02). Lactate increased after CPB in both groups but during reperfusion the control group had significantly more prolonged hyperlactataemia (p = 0.04). S-100B did not differ between groups. Indices of ventricular function did not differ. There was a tendency to improved lung compliance (p = 0.07), and pulmonary resistance changed less in the rIPC than in the control group during reperfusion (p = 0.02). Subsequently, peak inspiratory pressure was lower (p = 0.001).

CONCLUSION

rIPC significantly attenuated clinically relevant markers of myocardial and pulmonary injury after CPB. Transient limb ischaemia as an rIPC stimulus has potentially important clinical applications.

Randomized Controlled Trial of the Effects of Remote Ischemic Preconditioning on Children Undergoing Cardiac Surgery

OBJECTIVES

We conducted a randomized controlled trial of the effects of remote ischemic preconditioning (RIPC) in children undergoing repair of congenital heart defects.

BACKGROUND

Remote ischemic preconditioning reduces injury caused by ischemia-reperfusion in distant organs. Cardiopulmonary bypass (CPB) is associated with multi-system injury. We hypothesized that RIPC would modulate injury induced by CPB.

METHODS

Children undergoing repair of congenital heart defects were randomized to RIPC or control treatment. Remote ischemic preconditioning was induced by four 5-min cycles of lower limb ischemia and reperfusion using a blood pressure cuff. Measurements of lung mechanics, cytokines, and troponin I were made pre- and postoperatively.

RESULTS

Thirty-seven patients were studied. There were 20 control patients and 17 patients in the RIPC group. The mean age and weight of the RIPC and control patients were not different (0.9 +/- 0.9 years vs. 2.2 +/- 3.4 years, p = 0.4; and 6.9 +/- 2.9 kg vs. 11.5 +/- 10 kg, p = 0.06). Bypass and cross-clamp times were not different (80 +/- 24 min vs. 88 +/- 25 min, p = 0.3; and 55 +/- 13 min vs. 59 +/- 13 min, p = 0.4). Levels of troponin I postoperatively were greater in the control patients compared with the RIPC group (p = 0.04), indicating greater myocardial injury in control patients. Postoperative inotropic requirement was greater in the control patients compared with RIPC patients at both 3 and 6 h (7.9 +/- 4.7 vs. 10.9 +/- 3.2, p = 0.04; and 7.3 +/- 4.9 vs. 10.8 +/- 3.9, p = 0.03, respectively). The RIPC group had significantly lower airway resistance at 6 h postoperatively (p = 0.009).

CONCLUSIONS

This study demonstrates the myocardial protective effects of RIPC using a simple noninvasive technique of four 5-min cycles of lower limb ischemia and reperfusion. These novel data support the need for a larger study of RIPC in patients undergoing cardiac surgery.

Lung Development and Susceptibility to Ventilator-induced Lung Injury

RATIONALE

Ventilator-induced lung injury has been predominantly studied in adults.

OBJECTIVES

To explore the effects of age and lung development on susceptibility to such injury.

METHODS

Ex vivo isolated nonperfused rat lungs (infant, juvenile, and adult) were mechanically ventilated where VT was based on milliliters per kilogram of body weight or as a percentage of the measured total lung capacity (TLC). In vivo anesthetized rats (infant, adult) were mechanically ventilated with pressure-limited VTs. Allocation to ventilation strategy was randomized.

MEASUREMENTS

Ex vivo injury was assessed by pressure-volume analysis, reduction in TLC, and histology, and in vivo injury by lung compliance, cytokine production, and wet- to dry-weight ratio.

MAIN RESULTS

Ex vivo ventilation (VT 30 ml.kg(-1)) resulted in a significant reduction (36.0 +/- 10.1%, p < 0.05) in TLC in adult but not in infant lungs. Ex vivo ventilation (VT 50% TLC) resulted in a significant reduction in TLC in both adult (27.8 +/- 2.8%) and infant (10.6 +/- 7.0%) lungs, but more so in the adult lungs (p < 0.05); these changes were paralleled by histology and pressure-volume characteristics. After high stretch in vivo ventilation, adult but not infant rats developed lung injury (total lung compliance, wet/dry ratio, tumor necrosis factor alpha). Surface video microscopy demonstrated greater heterogeneity of alveolar distension in ex vivo adult versus infant lungs.

CONCLUSION

These data provide ex vivo and in vivo evidence that comparable ventilator settings are significantly more injurious in the adult than infant rat lung, probably reflecting differences in intrinsic susceptibility or inflation pattern.

Aerosol delivery of an enhanced helper-dependent adenovirus formulation to rabbit lung using an intratracheal catheter

BACKGROUND

Poor transduction of the ciliated airway epithelium and inefficient airway delivery of viral vectors are common difficulties encountered in lung gene therapy trials with large animals and humans.

METHODS

We delivered a helper-dependent adenovirus vector, incorporating a human epithelial cell-specific expression cassette, to rabbit lung. An intratracheal device was used to aerosolize a moderate dose of virus (5 x 10(11) particles), mixed with the enhancing agent LPC (L-alpha-lysophosphatidylcholine), directly into the airways. Lung mechanics, body weight and temperature, transgene expression and histopathology were studied at day 5.

RESULTS

Transgene expression was seen in the epithelium of large and small airways, from trachea to terminal bronchioles, with a strong tendency toward the right lung. All cell types of the surface epithelium were transduced. Extensive transduction of the epithelium (66% of cells in trachea) was obtained using virus formulated in isotonic 0.1% LPC, while virus formulated in 0.01% LPC transduced fewer cells (24% in trachea). A transient decrease in dynamic lung compliance was observed immediately following aerosol delivery. Fever and mild-to-moderate patchy pneumonia without edema were also observed.

CONCLUSION

These data demonstrate a strategy for efficient and effective transduction of airway epithelium in a large animal.

Fluorocarbons facilitate lung recruitment

OBJECTIVE

"Open the lung and keep it open" is increasingly accepted as a fundamental principle for mechanical ventilation. However, it is sometimes very difficult, or impossible, to recruit the diseased lung. We questioned whether one could facilitate recruitment by using a low dose of fluorocarbon in a model previously shown to be non-recruitable by conventional sustained inflation maneuvers.

DESIGN AND SETTING

Experimental prospective study in a university laboratory.

ANIMALS AND INTERVENTIONS

Nine saline-lavaged rabbits subjected to prolonged large tidal volume mechanical ventilation to establish significant lung injury were randomly allocated to two groups: control [High Frequency Oscillation (HFO) alone: n=4] or 1 ml/kg fluorocarbon (FC) treated (HFO/FC: n=5) for 2+1 h (experiment 1). An additional four similarly prepared animals were treated by single-lung instillation of 0.5 ml/kg dose of fluorocarbon and underwent serial computerized tomography scans at a series of predetermined step-wise pressure increase in both lungs (experiment 2).

MEASUREMENTS AND RESULTS

In experiment 1 there was a very significant improvement in oxygenation in HFO/FC group (PaO(2) increased from 108 mmHg to 424+/-81 mmHg; P<0.05) while there was no significant change in the control group. In experiment 2 lung volumes were determined using three-dimensional reconstruction. The lung having fluorocarbon showed a 2.4-fold increase in lung volume at inflation pressure of 15 cmH(2)O compared to the lung without fluorocarbon.

CONCLUSIONS

We propose that the low equilibrium surface tension and positive spreading coefficient of fluorocarbon facilitates lung recruitment by ungluing adherent surfaces in this model of lung injury.

Novel method to quantify loss of heart rate variability in pediatric multiple organ failure

OBJECTIVE

To develop a power-law model for measurement of heart rate variability (HRV) and to compare this model with established methods for measuring HRV in a group of children with organ failure (OF).

DESIGN

Prospective, observational study.

SETTING

Pediatric intensive care unit of a tertiary children's hospital.

PATIENTS

A total of 104 measurements were made on 50 patients (median age, 8 months; range, 2 days to 16 yrs) and categorized into three groups according to the number of simultaneous organs failing: 0-1 OF, 2 OF, and >/=3 OF.

INTERVENTIONS

Heart rate was recorded over a 5-min period when patients were hemodynamically stable. The power-law model represents a power function relating frequency distribution to magnitude of effect (in this case, squared deviation from the mean heart rate). Plotting the data on a bi-logarithmic scale produces a regression line for each measurement, described in terms of r2, slope, and x-intercept. Comparison with other HRV measures included two time-domain measures (sd of the normal R-R intervals and the square root of the mean squared differences of successive normal R-R intervals), one frequency-domain method (power spectral analysis), and one nonlinear method (detrended fluctuation analysis).

MEASUREMENTS AND RESULTS

For the power-law model, patients exhibited a similar r2 of.87 (.09) (mean [sd]) and slope of -1.80 (0.29), regardless of the degree of OF. HRV could thus be described purely in terms of x-intercept, which demonstrated a left shift with increasing OF (p <.001). This was independent of age and heart rate. Loss of HRV with increasing OF was demonstrated by all methods; however, only the power-law model was able to discriminate between each OF group. Using the model, change in HRV in individual patients over successive days often concurred qualitatively with the change in OF status.

CONCLUSION

The power-law model is an appropriate measure of HRV in pediatric patients, being neither age nor heart rate sensitive. Loss of HRV occurs with increasing OF; this effect was better demonstrated by the model compared with other measures of HRV.

Fibroblast growth factor receptor-1 and neonatal compensatory lung growth after exposure to 95% oxygen

Neonatal rats exposed to 95% oxygen (O2) for 7 days from birth had inhibited lung growth, DNA synthesis, and secondary septation. These parameters were rapidly restored by a period of recovery in air. Northern and Western blot analysis and immunohistochemistry were used to screen for the fibroblast growth factor receptor-1 (FGF-R1) and its high affinity ligand, basic fibroblast growth factor (bFGF), which could have a role in this recovery process. Expression of bFGF in the lung was significantly reduced at the end of the 7-day exposure to 95% O2 and was increased after 3 days of recovery in air. Expression of FGF-R1 was not affected by exposure to 95% O2 or recovery in air. We hypothesized that the increase in bFGF after removal from 95% O2, acting through the FGF-R1, would be critical for compensatory growth. Intraperitoneal injection of soluble truncated FGF-R1 at the onset of the recovery phase arrested compensatory lung DNA synthesis and secondary septation seen in control animals after 3 days of recovery, confirming a role for FGF-R1 in this model of compensatory neonatal lung growth.

Effect of air and heliox as carrier gas on CO2 transport in a model of high-frequency oscillation comparing two oscillators

OBJECTIVE

To study the effect of carrier gas on CO(2) transport during high-frequency oscillatory ventilation in a closed model.

DESIGN

In vitro model study.

SETTING

Respiratory research laboratory affiliated with a tertiary center for pediatric critical care.

SUBJECT

In vitro, closed-lung model consisting of a glass tube (9.8 x 1000 mm) covered at each end with balloons.

INTERVENTION

Air or heliox (80:20) at constant pressure was oscillated inside the model, comparing the Sensormedics 3100A and Hummingbird BMO-20N oscillators at equal amplitude.

MEASUREMENTS AND MAIN RESULTS

Tracer gas (CO(2)) was injected at one end of the model, and CO(2) concentration was measured at the opposite end. Speed of CO(2) transport was expressed as the time for the CO(2) concentration to reach 63% of the final concentration (the time constant). In room air, using the Hummingbird oscillator and increasing frequency stepwise from 5 to 20 Hz, the time constant decreased from 2813 to 457 secs (p =.05). Using the Sensormedics oscillator in room air at increasing frequency from 5 to 15 Hz, the time constant decreased from 1584 to 551 secs (p =.05). In heliox, using the Hummingbird oscillator, the speed of CO(2) transport increased by 85% (p =.029) at 5 Hz and by 28% (p =.05) at 15 Hz. With the Sensormedics oscillator using heliox, the speed of CO(2) transport increased by 16% at 5 Hz (p =.009) and 52% at 15 Hz (p =.008). Proportionally, the increase in CO(2) transport with heliox was greater at 5 Hz for the Hummingbird oscillator and at 15 Hz for the Sensormedics oscillator.

CONCLUSIONS

In a closed model, we showed that during high-frequency oscillatory ventilation in room air, CO(2) transport increases with increasing frequency for both ventilators. Using heliox as carrier gas significantly augmented CO(2) transport, but the increase is frequency and device dependent. The effect of heliox on oscillator performance and the clinical applicability of our findings require further study.

Comparison of loss in lung volume with open versus in-line catheter endotracheal suctioning

OBJECTIVE

Disconnecting the endotracheal tube from the ventilator causes significant loss in lung volume, which is further exacerbated by suctioning. In-line catheter suction systems have putative benefits over open catheter suction by maintaining positive pressure, thereby minimizing hypoxemia and hemodynamic instability. However, there is a theoretical risk of generating large negative airway pressures and auto-cycling of the ventilator with in-line catheter suction systems. We studied the effects on lung volume with both these techniques.

DESIGN

Open, randomized, crossover, clinical trial.

SETTING

Pediatric critical care unit.

PATIENTS

Fourteen paralyzed patients, age 6 days to 13 yrs.

INTERVENTIONS

Each patient, acting as his or her own control, was suctioned with an in-line catheter suction system and open catheter suction. Each suction maneuver was standardized. Changes in lung volume were measured by inductance plethysmography. Heart rate, blood pressure, and oxygen saturation were continuously monitored.

MEASUREMENTS AND MAIN RESULTS

Total lung volume loss was greater with open catheter suction compared with in-line catheter suction systems (p = .008). The most significant amount of lung volume loss associated with open catheter suction appears to be related to ventilator disconnection, rather than actual suctioning. Patients with decreased pulmonary compliance (< 0.8 mL/cm H2O/kg) demonstrated a greater loss in lung volume, both absolute and relative, as a result of ventilator disconnection (p = .038 and .006, respectively). Patients suctioned with open catheter suction desaturated to a greater extent than patients suctioned with in-line catheter suction (p = .026). There was evidence of ventilator triggering during the actual suction maneuver in all patients during in-line catheter suctions.

CONCLUSIONS

The most significant loss in lung volume during suctioning occurs primarily during ventilator disconnection. Hence, open catheter suction results in greater lung volume loss when compared with in-line catheter suction. We suggest that in-line catheter suction is preferable, especially in patients with significant lung disease and who require high positive end-expiratory pressures, to avoid alveolar derecruitment and exacerbating hypoxemia during endotracheal tube suctioning.

Gadolinium chloride inhibits pulmonary macrophage influx and prevents O(2)-induced pulmonary hypertension in the neonatal rat

Newborn rats exposed to 60% O(2) for 14 d demonstrated a bronchopulmonary dysplasia-like lung morphology and pulmonary hypertension. A 21-aminosteroid antioxidant, U74389G, attenuated both pulmonary hypertension and macrophage accumulation in the O(2)-exposed lungs. To determine whether macrophage accumulation played an essential role in the development of pulmonary hypertension in this model, pups were treated with gadolinium chloride (GdCl(3)) to reduce lung macrophage content. Treatment of 60% O(2)-exposed animals with GdCl(3) prevented right ventricular hypertrophy (p < 0.05) and smooth muscle hyperplasia around pulmonary vessels, but had no effect on morphologic changes in the lung parenchyma. In addition, GdCl(3) inhibited 60% O(2)-mediated increases in endothelin-1, 8-isoprostane, and nitrotyrosine residues. Organotypic cultures of fetal rat distal lung cells were subjected to cyclical mechanical strain to assess the potential role of GdCl(3)-induced blockade of stretch-mediated cation channels in these effects. Mechanical strain caused a moderate increase of endothelin-1 (p < 0.05), which was unaffected by GdCl(3), but had no effect on 8-isoprostane or nitric oxide synthesis. A critical role for endothelin-1 in O(2)-mediated pulmonary hypertension was confirmed using the combined endothelin receptor antagonist SB217242. We concluded that pulmonary macrophage accumulation, in response to 60% O(2), mediated pulmonary hypertension through up-regulation of endothelin-1.

4A randomized trial of prolonged prone positioning in children with acute respiratory failure

STUDY OBJECTIVE

To compare the effect of the prone position (PP) vs supine position (SP) on oxygenation in children with acute respiratory failure (ARF).

DESIGN

Prospective, randomized controlled trial.

SETTING

A 36-bed pediatric critical-care unit in a tertiary-care, university-based children's hospital.

PATIENTS

Ten children (mean [SD] age, 5 +/- 3.6 years) with ARF with a baseline oxygenation index (OI) of 22 +/- 8.5.

INTERVENTIONS

Following a period of stabilization in the SP, baseline data were collected and patients were randomized to one of two groups in a two-crossover study design: group 1, supine/prone sequence; group 2, prone/supine sequence. Each position was maintained for 12 h. Lung mechanics and acute response to inhaled nitric oxide were examined in each position.

MEASUREMENTS AND MAIN RESULTS

OI was significantly better in the PP compared to the SP over the 12-h period (analysis of variance, p = 0.0016). When patients were prone, a significant improvement in OI was detected (7.9 +/- 5.3; p = 0.002); this improvement occurred early (within 2 h in 9 of 10 patients) and was sustained over the 12-h study period. Static respiratory system compliance and resistance were not significantly affected by the position change. Inhaled nitric oxide had no effect on oxygenation in either position. Urine output increased while prone, resulting in a significantly improved fluid balance (+ 6.6 +/- 15.2 mL/kg/12 h in PP vs + 18.9 +/- 13.6 mL/kg/12 h in SP; p = 0.041). No serious adverse effects were detected in the PP.

CONCLUSION

In children with ARF, oxygenation is significantly superior in the PP than in the SP. This improvement occurs early, remains sustained for a 12-h period, and is independent of changes in lung mechanics.

Endothelin-1 and O2-mediated pulmonary hypertension in neonatal rats: a role for products of lipid peroxidation

We hypothesized that reactive O2 species, or their intermediary products, generated during exposure to elevated O2 lead to pathologic endothelin-1 expression in the newborn lung. Endothelin-1 expression and 8-isoprostane content (an in vivo marker of lipid peroxidation) were examined and found to be elevated (p < 0.05) in the lungs of newborn rats with abnormal lung morphology and pulmonary hypertension, as assessed by right ventricular hypertrophy, after a 14-d exposure to 60% O2. The antioxidant and lipid hydroperoxide scavenger, U74389G (10 mg/kg), given by daily i.p. injection prevented O2-dependent right ventricular hypertrophy (p < 0.05 compared with vehicle-treated controls), but had no effect on abnormal lung morphology. Additionally, we observed that 8-isoprostane caused marked endothelin-1 mRNA up-regulation in vitro in primary rat fetal lung cell cultures. We conclude that reactive O2 species, or their bioactive intermediaries, are causative in O2-mediated pulmonary hypertension and endothelin-1 up-regulation. It is likely that the bioactive lipid peroxidation product, 8-isoprostane, plays a key role in pathologic endothelin-1 expression and pulmonary hypertension during oxidant stress.

[High frequency oscillation ventilation compared to conventional mechanical ventilation plus exogenous surfactant replacement in rabbits]

OBJECTIVES: (a) to evaluate the effect on oxygenation and ventilation of rabbits with induced surfactant depletion when they are submitted to a conventional mechanical ventilation, plus a small dose of exogenous surfactant; (b) to compare this group with another group submitted to a High Frequency Oscillation (HFO) without exogenous surfactant administration.METHODS: Twenty New Zealand White rabbits weighing (-/+ 3 kg) were anaesthetized and artificially induced to a endogenous surfactant depletion by successively lung lavage with normal saline (aliquots of 25 ml/kg) until to reach a persistent PaO(2) less than 100 mmHg when submitted to a mechanical ventilation in a pressure control mode with a target tidal volume of 10ml/kg, PEEP of 5cm H(2)O, FiO(2) 1.0, respiratory rate 30/min, and inspiratory time of 0.65 s. Then the rabbits were divided in (a) CMV+S group, submitted to a conventional mechanical ventilation plus exogenous surfactant replacement; (b) HFO group, submitted to a High Frequency Oscillation Ventilation. Arterial blood gases were measured at control period, post lung lavage, 15, 16 and 120 minutes after treatment started. The groups were compared using Student t test.RESULTS: The post lung lavage PaO(2) in both groups was lower than 50mmHg (p=0.154), increasing after 15 min of treatment to 254 mmHg (CMV+S) and 288 mmHg (HFO, p=0.626). The PaO(2) at 60 and 120 minutes were higher (p=0.001) in the HFO group (431 e 431 mmHg) when compared with the CMV+S group, which showed a progressive fall (148 e 126 mmHg). At 60 minutes of treatment, the PaCO(2) was lower (p=0.008) in the CMV+S group (29 versus 41 mmHg).CONCLUSIONS: In ARDS animal model a protect mechanical ventilation strategy as HFO by itself promotes a fast and persistent increase in the oxygenation, with superior levels than those observed in animals treated with conventional mechanical ventilation plus exogenous surfactant replacement.

Distribution of pulmonary blood flow in the perfluorocarbon-filled lung

OBJECTIVE

Partial liquid ventilation (PLV) improves gas exchange in animal studies of lung injury. Perfluorocarbons (PFCs) are heavy liquids and are therefore preferentially delivered to the most dependent areas of lung. We hypothesised that improved oxygenation during PLV might be the consequence of a redistribution of pulmonary blood flow away from poorly ventilated, dependent alveoli, leading to improved ventilation/perfusion (V/Q) matching. This study investigated whether partially filling the lung with PFC would result in a redistribution of pulmonary blood flow.

DESIGN

Prospective experimental study.

SETTING

Hospital research institute laboratory.

PARTICIPANTS

Six anaesthetised pigs without lung injury.

INTERVENTIONS

Animals were anaesthetised and ventilated (gas tidal volume 12 ml/kg, PEEP 5, FIO2 1.0, rate 16). Whilst the pigs were maintained in the supine position, regional pulmonary blood flow was measured during conventional gas ventilation and repeated during PLV. Flow to regions of lung was determined by injection of radioactive microspheres (Co(57), Sn(113), Sc(46)). Measurements were performed with ventilation held at end-expiratory pressure and, in two PLV animals only, repeated with ventilation held at peak inspiratory pressure.

RESULTS

During conventional gas ventilation, blood flow followed a linear distribution with the highest flow to the most dependent lung. In the lung partially filled with PFC a diversion of blood flow away from the most dependent lung was seen (p = 0.007), resulting in a more uniform distribution of flow down the lung (p = 0.006). Linear regression analysis (r2 = 0.75) also confirmed a difference in distribution pattern. On applying an inspiratory hold to the liquid-containing lung, blood flow was redistributed back towards the dependent lung.

CONCLUSIONS

Partially filling the lung with PFC results in a redistribution of pulmonary blood flow away from the dependent region of the lung. During PLV a different blood flow distribution may be seen between inspiration and expiration. The clinical significance of these findings has yet to be determined.

Lung recruitment and lung volume maintenance: a strategy for improving oxygenation and preventing lung injury during both conventional mechanical ventilation and high-frequency oscillation

OBJECTIVE

To determine whether using a small tidal volume (5 ml/kg) ventilation following sustained inflation with positive endexpiratory pressure (PEEP) set above the critical closing pressure (CCP) allows oxygenation equally well and induces as little lung damage as high-frequency oscillation following sustained inflation with a continuous distending pressure (CDP) slightly above the CCP of the lung.

MATERIAL AND METHODS

Twelve surfactant-depleted adult New Zealand rabbits were ventilated for 4 h after being randomly assigned to one of two groups: group 1, conventional mechanical ventilation, tidal volume 5 ml/kg, sustained inflation followed by PEEP > CCP; group 2, high-frequency oscillation, sustained inflation followed by CDP > CCP.

RESULTS

In both groups oxygenation improved substantially after sustained inflation (P < 0.05) and remained stable over 4 h of ventilation without any differences between the groups. Histologically, both groups showed only little airway injury to bronchioles, alveolar ducts, and alveolar airspace, with no difference between the two groups. Myeloperoxidase content in homogenized lung tissue, as a marker of leukocyte infiltration, was equivalent in the two groups.

CONCLUSIONS

We conclude that a volume recruitment strategy during small tidal volume ventilation and maintaining lung volumes above lung closing is as protective as that of high-frequency oscillation at similar lung volumes in this model of lung injury

The open lung during small tidal volume ventilation: concepts of recruitment and "optimal" positive end-expiratory pressure

OBJECTIVES

To test the hypotheses that during small tidal volume ventilation (5 mL/kg) deliberate volume recruitment maneuvers allow expansion of atelectatic lung units and that a high positive end-expiratory pressure (PEEP) above the lower inflection point of the pressure/volume (PV) curve is not necessarily required to maintain recruited lung volume in acute lung injury.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

An animal laboratory in a university setting.

SUBJECTS

Adult New-Zealand rabbits.

INTERVENTIONS

We studied a) the relationship of dynamic loops during intermittent positive pressure ventilation to the quasi-static PV curve, and b) the effect of lung recruitment on oxygenation, end-expiratory lung volume (EELV), and dynamic compliance in two groups (n = 4 per group) of lung-injured animals (lung lavage model): 1) the sustained inflation group, which received ventilation after a recruitment maneuver (sustained inflation); and 2) the control group, which received ventilation without any lung recruitment.

MEASUREMENTS AND MAIN RESULTS

In the presence of PV hysteresis, a single sustained inflation to 30 cm H2O boosted the ventilatory cycle onto the deflation limb of the PV curve. This resulted in a significant increase in EELV, oxygenation, and dynamic compliance despite equal PEEP levels used before and after the recruitment maneuver. Furthermore, after a single sustained inflation, oxygenation remained high over 4 hrs of ventilation when a PEEP above the critical closing pressure of the lungs, defined as "optimal" PEEP, was used and was significantly higher compared with that in the control group ventilated at equal PEEP without preceding lung recruitment.

CONCLUSIONS

The observation that ventilation occurs on the deflation limb of the tidal cycle-specific PV curve allows placement of the ventilatory cycle, by means of a recruitment maneuver, onto the deflation limb of the PV envelope of the optimally recruited lung. This strategy ensures sufficient lung volume recruitment to maintain the lungs during the tidal cycle while using relatively low airway pressures.

Lung disease in mice with cystic fibrosis

The leading cause of mortality and morbidity in humans with cystic fibrosis is lung disease. Advances in our understanding of the pathogenesis of the lung disease of cystic fibrosis, as well as development of innovative therapeutic interventions, have been compromised by the lack of a natural animal model. The utility of the CFTR-knockout mouse in studying the pathogenesis of cystic fibrosis has been limited because of their failure, despite the presence of severe intestinal disease, to develop lung disease. Herein, we describe the phenotype of an inbred congenic strain of CFTR-knockout mouse that develops spontaneous and progressive lung disease of early onset. The major features of the lung disease include failure of effective mucociliary transport, postbronchiolar over inflation of alveoli and parenchymal interstitial thickening, with evidence of fibrosis and inflammatory cell recruitment. We speculate that the basis for development of lung disease in the congenic CFTR-knockout mice is their observed lack of a non-CFTR chloride channel normally found in CFTR-knockout mice of mixed genetic background.

Concealed air leak associated with large tidal volumes in partial liquid ventilation

Current ventilator strategies aim at maintaining an open lung and limiting both peak inspiratory pressures and tidal volumes to avoid alveolar distension. Perfluorocarbons, as well as being excellent solvents for oxygen and carbon dioxide, have the unique properties of being able to recruit dependent lung regions and improve pulmonary mechanics. Optimal ventilator strategies for partial liquid ventilation (PLV) have not yet been clearly defined. In the surfactant-depleted rabbit model, an approach involving a large tidal volume (VT) (15 ml/kg) and lung filled to FRC with perfluorocarbon (PFC) was compared with strategies involving a moderate VT (9 ml/kg) and partially filled lung (6 ml/kg), a moderate VT (9 ml/kg) and lung filled to FRC with PFC, and a large VT (15 ml/kg) and partially filled lung (6 ml/kg). PEEP was maintained at 5 cm H2O except in the moderate VT, partial-filling group, in which a PEEP of 9 cm H2O was used to maintain the rabbits for the duration of the experiment. Oxygenation was satisfactory in all groups, and peak inspiratory pressures were not significantly different. However, five of the 13 animals in the large-VT, PFC-filled lung group died of a pneumothorax prior to completion of the experiment. Of the eight animals in this group surviving the experiment, two had radiographic evidence of pneumothoraces, with an additional three animals having autopsy evidence of air leak. Of the 22 animals in the other groups, all survived with the exception of a single rabbit in the large VT, partial-filling group, which had both radiographic and autopsy evidence of air leak. We conclude that there is a significant risk of barotrauma in a PLV strategy in which a large VT is used in association with a lung filled to FRC with perfluorocarbon. Adequate gas exchange can be achieved with alternative ventilation strategies in combination with PLV.

Phenotypic abnormalities in long-term surviving cystic fibrosis mice

Mouse models for cystic fibrosis (CF) with no CFTR function (Cftr-/-) have the disadvantage that most animals die of intestinal obstruction shortly after weaning. The objective of this research was to extend the lifespan of CF mice and characterize their phenotype. Weanlings were placed on a nutrient liquid diet, and histologic and functional aspects of organs implicated in the disease were subsequently examined. Approximately 90% of Cftr-/- mice survived to 60 d, the majority beyond 100 d. Cftr-/- mice were underweight and had markedly abnormal intestinal histology. The intestinal epithelia did not respond to challenges with agents that raised intracellular cAMP, consistent with the absence of functional CFTR. No lesions or functional abnormalities were evident in the lungs. Liquid-fed Cftr-/- mice were infertile, although some males weaned to a solid diet were fertile before they died. Thus, we have succeeded in using dietary means to prolong the lives of Cftr-/- mice.

Changes in structure, mechanics, and insulin-like growth factor-related gene expression in the lungs of newborn rats exposed to air or 60% oxygen

Exposure of neonatal rats to > or = 95% O2 for 2 wk, a widely used model of oxidant/antioxidant interactions in neonatal lung injury, results in arrested lung growth without the dysplastic lesions observed in chronic human neonatal lung injury. To determine whether dysplastic lung cell growth would be seen at lesser O2 concentrations, we exposed newborn rats to either 95% O2 for 1 wk followed by 60% O2 for 1 wk, or to 60% O2 for 2 wk. Exposure to 95% O2 for 1 wk profoundly inhibited lung DNA synthesis. Recovery of synthesis did not occur during the 2nd wk in 60% O2, nor were areas of dysplastic growth evident in lung tissue. In contrast, a continuous 2-wk exposure to 60% O2 resulted in a slight increase in lung weight with a significant reduction in lung volume over a range of inflation pressures. Also seen was an overall, but inhomogeneous, reduction in lung cell DNA synthesis. A preliminary analysis of affected cell types suggested that inhibition of DNA synthesis affected endothelial cells more than interstitial cells, whereas DNA synthesis increased in type II pneumocytes. Areas of reduced DNA synthesis were interspersed with patchy areas of parenchymal thickening and active DNA synthesis. These areas of parenchymal thickening, but not other areas, had increased immunoreactive IGF-I and the type I IGF receptor. These data are consistent with a direct effect of O2 on growth factor and growth factor receptor expression in causing dysplastic lung cell growth in chronic neonatal lung injury.

Compliance of the respiratory system in newborn infants pre- and postsurfactant replacement therapy

Surfactant administration causes a rapid and dramatic improvement in gas exchange, but paradoxically, studies have failed to show an improvement in the mechanical properties of the lung. We have measured dynamic and static (passive flow-volume technique) compliance before and after a single dose of bovine lipid extract surfactant in 22 premature infants with RDS. This had no effect on the measured dynamic compliance. In contrast, surfactant significantly increased static compliance from 0.41 +/- 0.02 to 0.55 +/- 0.04 mL/cm H2O/kg. This improvement was the result of a substantial recruitment of lung volume after surfactant administration. This led us to reduce ventilator pressures, which produced an increase in both dynamic and static compliance, but did not recruit additional volume. We conclude that surfactant causes a substantial increase in static compliance due to volume recruitment, which is consistent with reports of increase in the measured FRC. However, despite this improvement, the compliance is still below our normal range.